1. Field of the Invention
The present invention relates to a GaN-containing semiconductor structure, more particularly to a GaN-containing semiconductor structure for GaN electronic device and the manufacturing method thereof.
2. Description of the Prior Art
Generally speaking, as for the manufacturing process of GaN-containing electronic device, high quality aluminum nitride (AlN) buffer layer is required to reduce the current leakage problem of electronic device. The AlN buffer layer can prevent the oxygen out-diffusion from the substrate, particularly from the sapphire substrate. In addition, the AlN buffer layer can also prevent the silicon (Si) diffusing from the silicon substrate or silicon carbide substrate into the GaN material.
However, due to the rough surface of AlN buffer and the large lattice constant mismatch between AlN and GaN material, GaN layer grown on AlN buffer will also suffer from having rough surface morphology.
In the prior art, during the growth process of AlN, the ammonia (NH3) is adjusted by entering the growth chamber periodically. The diffusion distance of aluminum atom on material surface can be increased by the method, and the surface of formed AlN will be a smooth surface. However, this method is complex and the growth control of AlN is difficult. In addition, this method will also reduce the growth rate of AlN. There is another problem that the quick and rapid on/off operation will cause the failure of the mass flow controller of metal organic chemical vapor deposition (MOCVD) or the mechanical shutter of molecular beam epitaxy (MBE).
In another prior art, other approaches comprise using extreme growth conditions in the MOCVD such as a very high growth temperature (>1200° C.) or a very low group V to group III gases flow ratio (V/III ratio, <10). However, most of the growth reactors cannot provide such high temperature and low V/III ratio. The extreme growth parameters may beyond the optimized range of growth conditions designed for most of the MOCVD reactors. As a consequence, the gas flow dynamics in the reactor will be significantly affected.
Sometime, an AlGaN buffer layer is also used to prevent the out-diffusion problem. However, it may not as effective as the AlN, because the AlGaN has lower bandgap. Thus, the impurity such as oxygen atom in this material will tend to form shallow donor and thus reduce the resistivity of the material. Its capability to trap impurities is also poorer as compared to AlN. Thus, the impurities may still diffuse into the GaN layer.